The U.S. Army officer demonstrating the M72 Light Anti-Tank Weapon stated that the projectile can penetrate armor plating up to 3/4 of an inch. M72 warheads, in real life, can penetrate up to five inches of armor plating.
When Harry finds the old ladies in the sex parlour they are copywriting a message on a board. Everything is in broken English except the perfectly placed possessive apostrophe in "customers' items" at the end of the message.
At the autopsy of the elderly security guard, the medical examiner says that the killer put his hand over the guard's mouth before stabbing him in the back, but as shown in the earlier scene the killer clearly didn't do this.
At the beginning of the film, before Harry goes into the restaurant, he drives by a lone red car parked at the corner. In the next shot, there is a white car, behind the red car, that wasn't in the first shot.
When Harry and his old partner are driving to the liquor store holdup, in the shot from the rear of the car through the windshield, Harry's partner is hanging on to the light with his left hand. In the very next shot, he is speaking on the radio with the same hand.
As the Police vehicles arrive at the Mustafa bust, the third squad car to arrive, number 167 blocks the intersection and its sole occupant gets out however moments later car 167 is seen again at the front of shot pulling up outside Mustafa's premises with a number of armed SWAT officers in it.
The mayor's limo screeches to a halt next to a truck and the baddies blow the truck to bits with their rocket launcher. In both long shots of the truck it is clearly not moving, but in the very brief head-on shot of the truck as the rocket hits its radiator, it is slowly moving forward.
When the Mayor is being kidnapped, while being carried away his vest is clearly unbuttoned (at approx. 1:10:25). The next cut scene, while still being carried away, the Mayor's vest is clearly back to being buttoned up (at approx. 1:10:33).
During the training session with the M72 LAW Rocket, Inspector Moore never would have been allowed to step behind the rocket tube, thus exposing her to the back-blast. Range Safety Officers would have made the area clear before allowing the operator to fire the rocket.
In the raid on Mustafa's hangout we see both SWAT and the regular officers with assault rifles. Regular police officers did not carry high powered rifles until after the North Hollywood shootout at the botched bank robbery in 1997. However, SFPD did not have a full time SWAT team then. Regular officers would carry the their SWAT gear in the patrol cars and deploy as needed. It is possible that the officers in regular uniforms could have been SWAT team members deploying from their patrol duties.
When Harry confronts the priest in his church (shortly before Harry's partner shoots the alleged "nun"), Harry pushes the priest forcefully backwards into the confessional. When the priest hits the 'tiled' rear wall, you can see it shake, revealing it to be a cardboard prop.
When Callahan fires the bazooka at the watch tower that Bobby Maxwell has just climbed up to, the cabin on top of the tower vanishes shortly before the missile hits it. We just see the bare platform for a few frames, then there's an explosion and then we see the platform in flames.